John J. Giannini of Potomac, a former customer service representative of the U.S. Postal Service, acknowledged yesterday that he is the federal employee referred to in one count of the indictment returned against the Rev. Guido John Carcich of the Pallottine Fathers.

Giannini, now a staff assistant to U.S. Sen. Jennings Randolph (D-W. Va.), said he testified before the grand jury in Baltimore on Tuesday. He denied any wrong doing and said prosecutors assured him that he was "not in trouble."

He said the language of the indictment, which indicates that Giannini had use of $20,000 in Pallottine funds "for some period of time," was confusing to him. "I don't want to talk about it now," he said.

Count 55 of the indictment charges that Carcich embezzled $20,000 on or about Nov. 3, 1970, and then permitted a federal employee to use the money. The indictment gave no indication of how long the federal employee had the money or for what it was intended to be used.

Giannini said he met Carcich in the 1960s as a part of his work as a customer relations specialist.Giannini was charged with encouraging volume users of the mails to employ the then-new zip code system. At the height of their activity, the Pallottines spent more than $1 million annually on postage to distribute the fund-raising sweepstakes scheme.

Carcich and Giannini remained friends after Giannini left the Post Office Department in August, 1971 to go to work for the Senate Post Office and Civil Service Committee. Giannini recalled he and Carcich once explored the idea of going into business together in the Boston area, but the idea did not work out. Giannini said the $20,000 referred to in the indictment was not related to that idea.

Giannini, who had been active in politics in his native West Virginia before going to work for the postal service, moved to Sen. Randolph's staff last year.